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weed species and three transplanted perennial ornamentals when it was added to pine bark potting mix and when it was applied to the surface of potting soil. Separate experiments evaluated potential causes of the herbicidal effect and measured the effect

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and Benson, 2001 ). The use of aerated steam to pasteurize soil or potting mixes to eradicate soilborne pathogens, weed seeds, and insects was pioneered by K.F. Baker (1957) . The principles of treating soil or potting media with heat at temperatures

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A soil cooling system was developed using a chest-type freezer as a central cold air reservoir. Thermostatically controlled fans circulate cold air from the freezer into smaller air chambers containing large plastic pots. The system is inexpensive, easily constructed, and provides good soil temperature control.

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Chrysanthemum morifolium Ramat ‘Fred Shoesmith’ was grown in a soil medium previously used to grow Easter lilies, Lilium longiflorum Thunb. ‘Ace’, treated with single drenches of a-cyclopropyl-a-(p-methoxyphenyl)-5-pyrimidine methanol (ancymidol) in early February and harvested April 26. Enough ancymidol was retained in the medium after 76 days of lily growth and 52 surface-irrigations to significantly retard chrysanthemum growth. Plant height after 10.5 weeks was about 12 and 29% less in media from 0.25- and 0.50-mg (active ingredient) ancymidol drench treatments, respectively, than in untreated medium. However, chrysanthemums grown in a new soil medium in new clay pots were about the same height as plants in new soil medium in pots from the 0.50-mg treatment, indicating that not enough ancymidol to retard chrysanthemum growth was retained in the clay pots.

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Ten mixtures of soil, sphagnum peat moss, pinebark, almond hulls, and sheep manure, and 8 combinations of clay loam and sand, 20cm deep, were examined for relevant physical properties and possible use as greenhouse potting composts under Cypriot greenhouse conditions. There were significant variations of bulk density, porosity, moisture content, air space and percolation rates. Comparison of these data with other workers’ information showed a linear relationship between bulk density and total pore space regardless of specific gravity. The rate of salt removal, as measured by effluent conductivity, was predictable from a knowledge of the starting salinity concentration, regardless of the potting mixture. The higher the percolation rate, the less efficient was salt removal, with the removal rate decreasing as the initial salt concentration decreased. Percolation rate showed an exponential relationship with the ratio of porosity to maximum moisture content, with percolation increasing markedly above a ratio of 1.8. Mixtures in excess of 0.70cm3 cm−3 total porosity showed markedly high percolation rates, requiring large water volumes to reduce salinity. It was the opinion of these authors that very porous potting mixtures would unnecessarily increase water utilization in a semi-arid climate, with problems in controlling salinity with trickle irrigation systems likely to be exacerbated.

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A double-tent solarization technique, which accumulates higher soil temperatures than solarization of open fields, was recently approved by the California Department of Food and Agriculture (CDFA) as a nematicidal treatment for container nurseries. Due to the need for broad-spectrum pest control in container nursery settings, this technique was tested to determine its usefulness as an herbicidal treatment. Laboratory-derived thermal death dosages (temperatur × time) for several weed species important in California, including common purslane (Portulaca oleracea), tumble pigweed (Amaranthus albus), and black nightshade (Solanum nigrum), were previously determined and the data were used as guidelines for devising treatment duration in this study. In two field experiments conducted in 1999 and 2000 to validate the laboratory data, moist soil was placed in black polyethylene planting bags [3.8 L (1 gal) volume], artificially infested with seeds of the three test species, and subjected to 0 to 24 hours of double-tent solarization after reaching a threshold temperature of 60 °C (140 °F) (about 1.5 to 2.0 h after initiation of the experiment). In 1999, samples were removed at 2, 4, 20, and 24 hours after reaching the 60 °C threshold, then incubated to ameliorate possible secondary dormancy effects. Seeds failed to germinate in any of the solarized treatments. In 2000, samples were removed at 0, 1, 2, and 6 h after reaching 60 °C. Again, apart from the nonsolarized control treatment, all weed seeds failed to germinate at any of the sampling periods, in accordance with prior laboratory thermal death results. Reference tests to estimate effects of container size on soil heating showed that soil in smaller container sizes (soil volume) reached higher temperatures, and were maintained at high temperature [above 60 °C (140 °F)] for a longer period of time, than larger container sizes. The double-tent solarization technique can be used by commercial growers and household gardeners to effectively and inexpensively produce weed-free soil and potting mixes in warmer climatic areas.

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Nine bean cultivars/lines were grown in a Tripp sandy-clay loam (high pH), a Sharpsburg silty clay loam (neutral pH), and a potting mix (equal volume of sand, soil [Sharpsburg silty clay loam], vermiculite and moss pest) (low pH) in greenhouse (one experiment), growth chamber (two experiments), and field (two experiments) in Lincoln, NE, in order to evaluate the leaf reaction of the plants to a Nebraska rust (Uromyces appendiculatus var. appendiculatus) isolate US85-NP-10-1. A factorial arrangement of soil media and cultivars/lines in a randomized complete block design was used in the greenhouse and growth chamber experiments, while a split-plot design (soil media as main plots and cultivars/lines as sub-plots) was used in the field experiments. Significant differences were observed for rust pustule size of cultivars/lines grown on the three different soil media. Plants grown on potting mix medium showed significant Increases in rust pustule size compared with Tripp (high pH) or Sharpsburg silty clay loam soils (neutral pH). A significant interaction occurred between soil media and cultivars/lines for the rust reaction. A positive correlation (R= +0.5) was observed between the increased concentration of C1 and Mn,, and a negative correlation for lower K (R+ -0.44) and soil pH in the potting mix and larger rust pustule size of leaves. These results have implications for plant breeders and pathologists involved in evaluating bean progenies and lines for rust resistance.

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Nine bean cultivars/lines were grown in a Tripp sandy-clay loam (high pH), a Sharpsburg silty clay loam (neutral pH), and a potting mix (equal volume of sand, soil [Sharpsburg silty clay loam], vermiculite and moss pest) (low pH) in greenhouse (one experiment), growth chamber (two experiments), and field (two experiments) in Lincoln, NE, in order to evaluate the leaf reaction of the plants to a Nebraska rust (Uromyces appendiculatus var. appendiculatus) isolate US85-NP-10-1. A factorial arrangement of soil media and cultivars/lines in a randomized complete block design was used in the greenhouse and growth chamber experiments, while a split-plot design (soil media as main plots and cultivars/lines as sub-plots) was used in the field experiments. Significant differences were observed for rust pustule size of cultivars/lines grown on the three different soil media. Plants grown on potting mix medium showed significant Increases in rust pustule size compared with Tripp (high pH) or Sharpsburg silty clay loam soils (neutral pH). A significant interaction occurred between soil media and cultivars/lines for the rust reaction. A positive correlation (R= +0.5) was observed between the increased concentration of C1 and Mn,, and a negative correlation for lower K (R+ -0.44) and soil pH in the potting mix and larger rust pustule size of leaves. These results have implications for plant breeders and pathologists involved in evaluating bean progenies and lines for rust resistance.

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Peat-sand (1:1, by volume) and wood-sand (2:1, by volume) mixes in 10 cm plastic pots were planted with Epipremnum aureum Linden & Andre cv. Tricolor (pothos), Coleus glumei Benth (coleus), and Brassaia actinophylla Endl. (schefflera). After the pH of the leachate had dropped to between 4.0 and 5.0, pots received a single irrigation with solutions NaHCO3 and KHCO3. For the peat mix, the highest concentrations (0.20 M) of NaHCO3 and KHCO3 raised the leachate pH to nearly 9.0; the pH subsequently dropped most rapidly in pots containing coleus and schefflera, and slowest with pothos. In pots containing the wood-sand mix, the pH climbed as high as 8.0 immediately after treatment with 0.08 m KHCO3, then decreased slowly in pothos and more rapidly with the other 2 species. In peat mixes, the final leachate pH was nearly one unit greater than the saturation paste pH of the soil. In wood-sand pots, mix from the bottom half of the pot was always lower in pH than mix from the top half. Except for schefflera the pH of the last leachate obtained was nearer the pH of the bottom half of the pot than that of the top half.

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Phytophthora ramorum, while thought to be primarily an aboveground pathogen, can be introduced into soilless potting media in the nursery industry as sporangia or chlamydospores and remain undetected while disseminated geographically. Inoculum of this pathogen, both North American (A-2 mating type) and European (A-1 mating type) isolates, was used to infest potting media components or soil, using either sporangia, chlamydospores produced in vermiculite culture, or dry infected `Nova Zembla' rhododendron (Rhododendron sp.) leaf pieces. Vermiculite chlamydospore/oospore inoculum of P. citricola, P. cactorum, and P. citrophthora were included for comparison. Survival was determined monthly by leaf disc baiting or direct plating on selective medium. Results indicated that P. ramorum survived in most media components or soil for up to 6 months when introduced as sporangia, or up to 12 months as chlamydospores. However, it was not detected at all from infected rhododendron leaf pieces by either detection method. These results show that P. ramorum can survive in potting media if introduced as sporangia or chlamydospores, and accordingly the pathogen could be disseminated geographically without being detected visually.

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